In general, the present invention relates to resin-fortified emulsion polymer compositions comprising a sugar-based vinyl monomer.
Emulsion Polymers
High molecular weight emulsion polymers are useful in the coatings and inks industry. However, high molecular weight emulsion polymer technology has some drawbacks. Problems associated with high molecular weight emulsion polymer systems include wetting and adherency problems, mechanical instability, freeze/thaw instability and inability to biodegrade or be repulped.
U.S. Pat. No. 4,151,143, issued to Blank, et al., discloses a surfactant-free polymer emulsion coating composition and a method for preparing the same. U.S. Pat. No. 4,179,417, issued to Sunada, et al., discloses a composition for water based paints containing a water soluble resin and a water dispersible polymer which are employed as water based paints and can optionally contain a cross linking agent. Canadian Pat. No. 814,528, issued Jun. 3, 1969, discloses low molecular weight alkali soluble resin, resin cuts and method of their preparation and purification. U.S. Pat. No. 4,820,762 discloses resin-fortified emulsion polymers that are created by addition of a low molecular weight support resin during the emulsion polymerization process.
Sugar-based Vinyl Monomers
U.S. Pat. No. 5,827,199 discloses copolymers prepared from alkyl polyglycoside maleic acid esters (sugar monomer) and vinyl monomers. These water borne copolymers contain sugar units in their polymeric structure introduced by way of the bifunctional sugar monomer. Acrylic copolymers containing around 10% sugar monomer have been found to be noninterfering in paper recycling, while copolymers containing at least 40% sugar monomer are biodegradable under composting conditions as per ASTM D5338 (see Adhesives Age 41(2):24, 1998).
The resin-fortified emulsion polymers of the present invention provide suitable mechanical, physical and performance properties when compared to conventional emulsion polymers and represent an advance in emulsion polymerization technology. It is an object of the present invention to provide novel copolymers that are useful in biodegradable, repulpable inks, primers coatings, overprint coatings and related products used on paper and paperboard, synthetic and natural polymer films, metallized films and metal foils and sheets, as well as combinations thereof. These printed or decorated substrates could be used in packaging, publication, commercial printing, wallpaper, specialty and other related applications.
Briefly, in accordance with the present invention, a resin-fortified emulsion polymer is prepared by exposing a resin to an emulsion polymerization reaction mixture comprising a sugar-based vinyl monomer and other vinyl comonomers. The resin is a low molecular weight polymer and is soluble or dispersible in water or alkali solutions. The emulsion polymerization reaction mixture contains any monomers employed in emulsion polymerization reactions and additionally comprises a sugar-based vinyl monomer. The resulting resin-fortified emulsion polymers have enhanced performance for coatings, ink and graphic art applications and are recycling friendly.
The present invention is both a method of obtaining a resin-fortified emulsion polymer comprising a sugar-based vinyl monomer and the polymer itself. When used herein the term xe2x80x9cemulsion polymerxe2x80x9d refers to any polymer prepared by emulsion polymerization. Such polymers are formed by the polymerization of one or more monomers capable of undergoing free radical emulsion polymerization. When used herein the term xe2x80x9cresinxe2x80x9d encompasses all low molecular weight resins of from about 500 to about 20,000, and preferably about 500 to 10,000, number average molecular weight which are soluble or dispirsible in water or alkali.
In practicing the present invention, a solution polymer support resin is exposed to an emulsion polymerization reaction mixture during the emulsion polymerization reaction.
Typically, the solution polymer support resin is first added to a reactor under an inert atmosphere. Water, surfactant and buffer are then added with agitation and brought to reaction temperature. A pre-emulsion is prepared separately by mixing together water, surfactant and the monomers including the sugar-based vinyl monomer. The pre-emulsion step is preferred because the sugar-based vinyl monomer may not be soluble in the monomers and may not form a single homogenous phase. A surfactant is required to cosolubilize the monomers and allow a homogenous feed to be fed to the reactor during the starve-fed polymerization process to ensure a random incorporation of the monomers. The charge initiator, preferably a water-soluble initiator, is added to the reactor followed immediately by the start of the pre-emulsion feed, which is fed to the reactor over an extended period of time, typically 1-2 hours. This is what is termed a xe2x80x9cstarve-fedxe2x80x9d emulsion process. Base (typically ammonium hydroxide, 30 wt % in water) is added simultaneously with the pre-emulsion to keep the emulsion slightly basic. A second initiator feed is added to the emulsion at the finish of the pre-emulsion feed. A final initiator feed is added one hour later as a chaser to scavenge any unreacted monomer. The emulsion is allowed to react an additional hour before it is cooled to room temperature.
In conducting the present emulsion polymerization reaction, standard emulsion polymerization techniques are employed with the addition of a pre-emulsion prepared by separately mixing together water, surfactant and the monomers and the addition of base along with the pre-emulsion to keep the emulsion slightly basic.
Standard nonionic and anionic surfactants are employed in the reaction. Advantageously, the reaction is conducted at an elevated temperature ranging from about 60xc2x0 to about 100xc2x0 C., at ambient pressure and under an inert atmosphere such as nitrogen. The reaction mixture is maintained under agitation employing standard mixing techniques.
Before the resin is mixed with the emulsion polymerization reaction mixture there must be a polymeric (or steric) stabilizer present in the reaction mixture to prevent coagulation of the emulsion particles. The stabilizer can be any of the conventional nonionic surfactants such as ethoxylated alkylphenols including ethoxylated nonylphenol having at least 20 ethylene oxide units, ethoxylated octylphenol having at least 20 ethylene oxide units or, alternatively, functional monomers such as acrylic acid, methacrylic acid or polyethylene glycol monomethacrylate. The stabilizer is added to the reaction mixture prior to resin addition and usually in amounts ranging from about 1 to about 8 percent by weight of the reaction mixture and preferably from about 2 to about 4 weight percent.
Suitable low molecular weight support resins employed in the practice of the present invention include any solution or bulk polymerized polymers prepared from ethylenically unsaturated monomers such as olefins, mono vinylidene aromatics, alpha, beta-ethylenically unsaturated carboxylic acids and esters thereof, and ethylenically unsaturated dicarboxylic anhydrides. They are known materials and are prepared employing standard solution polymerization techniques. Preferably, the support resins are prepared in accordance with the teachings of U.S. Pat. No. 4,414,370, U.S. Pat. No. 4,529,787 and U.S. Pat. No. 4,456,160 all of which are incorporated herein by reference.
Other suitable commercially available resins include water dispersed or water dispersible aliphatic polyurethanes such as Spensol L52 an aliphatic polyurethane commercially available from Reichhold Chemical, Inc., and water dispersible silicone ethylene oxide copolymers such as FF400, a water dispersible silicone-ethylene oxide copolymer commercially available from Dow Corning. These and other similar resins can be used especially where the desirable characteristics of the resin, i.e., flexibility, slip properties, durability, etc., are required. These resins should be low molecular weight with a number average molecular weight of from about 500 to 20,000.
Preferred support resins include those resins containing styrene (ST), alpha methylstyrene (AMS), acrylic acid (AA) and mixtures thereof. An especially preferred support resin is a ST/AA copolymer containing three parts ST and one part AA and which has a number average molecular weight of from about 1,000 to about 6,000 and, preferably, from about 2,000 to about 4,000.
Suitable monomers employed in the preparation of the support resins include acrylic acid, methacrylic acid, styrene, alpha-methylstyrene, hydroxyethylmethacrylate and esters of acrylic acid and methacrylic acid.
As noted above, the resins useful in the process of the present invention should be low molecular weight with a number average molecular weight in the range of from about 500 to about 20,000, preferably about 500 to about 10,000 and optimally about 2,000 to about 4,000. Also the resins must be water soluble or water dispersible either as is or in an alkaline medium such as ammonium hydroxide.
The monomers employed in the preparation of the present emulsion polymers are any monomers used in emulsion polymerization reactions. Suitable monomers include ethylenically unsaturated monomers such as olefins, mono vinylidene aromatics, alpha, beta ethylenically unsaturated carboxylic acids and esters thereof, ethylenically unsaturated dicarboxylic anhydrides and halo substituted olefinics. Preferred monomers include methylmethacrylate (MMA), styrene (ST), alphamethylstyrene (AMS), acrylic acid (AA), methacrylic acid (MAA), butylmethacrylate (BMA), butylacrylate (BA), 2-ethylhexylacrylate (2-EHA), ethylacrylate (EA), hydroxyethylacrylate (HEA) and hydroxyethylmethacrylate (HEMA).
Suitable sugar-based vinyl monomers are described in U.S. Pat. 5,872,199. It is preferable for the monomer to have an average degree of polymerization (DP) equal to 1.2 to 2.0, and an average degree of substitution (DS) equal to 2.
When used herein, the term xe2x80x9csugar-based vinyl monomerxe2x80x9d refers to an alkyl polyglycoside maleic acid ester with the formula 
wherein Glu is a saccharide moiety; R is selected from the group consisting of a C1 to C30 alkyl or mixtures thereof; Rxe2x80x2xe2x80x3 is selected from the group consisting of hydrogen, a C1 to C30 alkyl or a mixture thereof, n is an integer of 0 to 10; x and y are integers of 0 to 3 or 0 to 4, where the maximum value of 3 or 4 for x and y equals the number of hydroxyls on the Glu moiety, but not both x and y are zero.
Especially preferred is the compound wherein Glu is derived from xcex1-D-glucose. Also especially preferred is the compound wherein R is selected from the group consisting of a C3 to C8 alkyl group or mixture thereof. We especially envision as useful compounds where Rxe2x80x2xe2x80x3 is selected from the group consisting of a hydrogen, H, a C8 to C18 alkyl group or mixture thereof and a compound prepared by estrification of alkyl polyglycoside maleic acid with a primary C1 to C30 alcohol or mixture thereof.
The sugar-based vinyl monomer was prepared by the method provided in Example 5 described in U.S. Pat. No. 5,872,199.
The support resin is added to the present emulsion polymerization reaction in amounts sufficient to modify the flow characteristics of the resulting emulsion polymer. Amounts ranging from about 2 to about 50 weight percent or more based on the total weight of solids in the emulsion polymerization reaction mixture are usually effective. Advantageously the support resin is added in amounts greater than about 5% and preferably greater than about 10% by total weight of solids in the emulsion reaction mixture. The optimum amount of support resin and sugar-based vinyl monomer to be added during the emulsion polymerization reaction will depend on a variety of factors, such as, the particular makeup of the support resin, the particular makeup of the sugar-based emulsion polymer, the end use application for the emulsion polymer, recyclability requirements of the emulsion polymer, and the environment in which the emulsion polymer will be used. One skilled in the art can readily determine the optimum amount of support resin and sugar-based vinyl monomer to be used in a particular application by conducting routine experiments.
A suitable polymer of the present invention can be designed to be recycling friendly, having either biodegradability or repulpability characteristics or both. The amount of sugar-based vinyl monomer can be optimized to provide the most desirable biodegradable and repulpable characteristics. Preferably, the amount of sugar-based vinyl monomer should be 2-40 wt %.
The present invention is also an ink, preferably comprising a pigment and a fortified emulsion polymer comprising a sugar-based vinyl monomer, a resin and at least one emulsion-polymerizable monomer. Preferred formulations are disclosed below in the Examples.